Final answer:
The sciatic nerve travels under the piriformis muscle and is the longest and thickest nerve in the body, originating from the sacral plexus.
Step-by-step explanation:
The sciatic nerve is a major nerve extending from the lower end of the spinal cord down the back of the thigh, and into the lower leg and foot. It is made up of the tibial and common fibular (peroneal) nerves, which split just above the knee. This nerve originates from the sacral plexus, a network of nerves in the pelvis, and travels under the piriformis muscle in the gluteal region. The sciatic nerve is the longest and thickest nerve in the body, and it is essential for movement and sensation in the thighs, legs, and feet.